Comparative overwintering physiology of Alaska and Indiana populations of the beetle Cucujus clavipes (Fabricius): roles of antifreeze proteins, polyols, dehydration and diapause

Abstract

SUMMARY The beetle Cucujus clavipes is found in North America over a broad latitudinal range from North Carolina (latitude ∼35°N) to near tree line in the Brooks Range in Alaska (latitude, ∼67°30′ N). The cold adaptations of populations from northern Indiana (∼41°45′N) and Alaska were compared and, as expected, the supercooling points (the temperatures at which they froze) of these freeze-avoiding insects were significantly lower in Alaska insects. Both populations produce glycerol, but the concentrations in Alaska larvae were much higher than in Indiana insects(∼2.2 and 0.5 mol l–1, respectively). In addition, both populations produce antifreeze proteins. Interestingly, in the autumn both populations have the same approximate level of hemolymph thermal hysteresis,indicative of antifreeze protein activity, suggesting that they synthesize similar amounts of antifreeze protein. A major difference is that the Alaska larvae undergo extreme dehydration in winter wherein water content decreases from 63–65% body water (1.70–1.85 g H2O g–1 dry mass) in summer to 28–40% body water(0.40–0.68 g H2O g–1 dry mass) in winter. These 2.5–4.6-fold reductions in body water greatly increase the concentrations of antifreeze in the Alaska insects. Glycerol concentrations would increase to 7–10 mol l–1 while thermal hysteresis increased to nearly 13°C (the highest ever measured in any organism) in concentrated hemolymph. By contrast, Indiana larvae do not desiccate in winter. The Alaska population also undergoes a diapause while insects from Indiana do not. The result of these, and likely additional, adaptations is that while the mean winter supercooling points of Indiana larvae were approximately –23°C, those of Alaska larvae were –35 to–42°C, and at certain times Alaska C. clavipes did not freeze when cooled to –80°C.